Systems and methods for optically sensing and decoding data are known to those skilled in the art. Portable systems are also known for optically sensing and decoding data. See U.S. Pat. No. 3,509,353 entitled Portable Record Reader by Sundblad et al., U.S. Pat. No. 3,716,699 entitled Method and Apparatus for Optical Code Reading by Eckert, Jr. et al., U.S. Pat. No. 3,736,410 entitled Hand Held Apparatus for Sensing Data Bits Carried on a Sheet by Ragland et al., U.S. Pat. No. 3,748,483 entitled Indicating Device for Use In Optical Sensing Equipment by Englund et al., U.S. Pat. No. 3,925,639 entitled Method and Apparatus for Reading Bar Coded Data Wherein a Light Source is Periodically Energized by Hester, U.S. Pat. No. 4,072,859 entitled Wand Turn-On Control by McWaters, and U.S. Pat. No. 4,160,156 entitled Method and Apparatus for Reading Bar Coded Data Wherein The Light Source Is Periodically Energized by Sherer.
Portable systems have been used for data collection in a broad range of operations, including inventory control in retail stores and in the tracking of packages or cargo in the delivery industry. Portable optical reading units are typically battery powered or attached to a terminal station which supplies a power source.
Codes have been produced, and printed on products or containers, to increase the accuracy of such data collection systems. One such code is a "bar code" which may be read by passing an optical sensing unit over the bar code on the product or by passing the product over the optical sensing unit. A bar code typically consists of a pattern of black and white bars of varying widths, with the encoded information determined by the sequence of these varying width bars. Bars are scanned by the optical sensing unit and the widths of the bars are then translated into a specific identifying sequence for that particular item.
An optical sensing unit typically requires a source of radiation to illuminate the bar coded data which normally places a significant drain on the battery. As the applications of these portable optical sensing units continue to expand, users of such units continue to demand lighter weight, lower cost, and extended usage time from these units. Hence, the amount of power used by the radiation source and the accompanying sensing and decoding circuits continue to be a major obstacle in expanding applications.
One patent which describes a low power bar code reader is U.S. Pat. No. 5,281,800 entitled Method and Apparatus for Low Power Optical Sensing and Decoding of Data and is assigned to the assignee of the present invention. As described, a light source is flashed at a low frequency until a bar code is placed in the optical path of the light source. The light source is then flashed at a higher frequency during the capture of bar code information. Bar codes are detected by producing a frequency modulated series of pulses which provide an indicator of the detected bar code. In an alternative embodiment, the output of a light detector may be quantized and applied to a resettable digital integrator to produce a direct digital output. A digital implementation of a pulse counting circuit is thereby provided. The '800 patent uses less power than the prior art, but may not save power during a bar code decoding sequence after the presence of a bar code has been detected in the optical path.
As portable bar code reading systems have become more widely used, systems have also been developed to instruct users in the operation of bar code scanners and to evaluate the print quality of bar codes. For example, U.S. Pat. No. 5,231,293 entitled Bar Code Reading Instrument Which Prompts Operator to Scan Bar Codes Properly to Longacre, Jr. discloses a bar code reading wand which prompts the user to scan faster, slower, or more evenly. A bar code is manually scanned to provide a bar code signal. The signal is then sampled in an analog to digital converter at a constant rate to provide successive data signal samples. The digital samples are stored by a central processing unit in a scan profile block of locations in a random access memory. The stored data samples are then used to determine if a code was properly received or if an instructive prompt is required for a re-scan.